Risks of Multiple Pregnancies

Introduction

Multiple pregnancies (for example, twin or triplet pregnancies) pose higher risks to pregnant people than singleton pregnancies. However, equipping yourself with knowledge and information can help minimise these risks and increase the chances of a healthy outcome in pregnancy. First, let’s define multiple pregnancies and their associated risks.

A multiple pregnancy means that a person assigned female at birth (AFAB) is pregnant with two or more babies. This happens either when more than one egg is fertilised (known as fraternal multiples) or when a sperm fertilises one egg which then splits into two or more embryos (identical multiples).¹ Multiple births make up only about three percent of all births. However, the number of multiple births has risen in recent decades due to the increased use of assisted reproductive technologies such as in-vitro fertilisation (IVF) in developed countries.²

The incidence of unidentical twins varies according to race and maternal age. Africans have the highest incidence of 10-40 per 1,000, 7-10 per 1,000 in Caucasians, and 3 per 1,000 in Asians, but the incidence of identical twins remains fairly constant at approximately 4 per 1,000 births.³

Types of multiple pregnancies

The most common types of multiple pregnancies are twin, fraternal (non-identical and also known as dizygotic), and identical twins. Fraternal twins occur when two separate eggs are fertilised by two separate sperm and implant in the uterus. By comparison, identical twins (also known as monozygotic) are formed when a single fertilised egg splits into two. Each embryo, in this case, is genetically identical to the other.

Other types of multiple pregnancies include triplets, quadruplets, and higher-order multiples like quintuplets, sextuplets, and so on. These can be a combination of identical or fraternal multiples. For example, triplets can be formed from three individual eggs (trizygotic), identical (when one egg divides into three embryos), or a combination of both fraternal and identical. 

Factors contributing to multiple pregnancies

The occurrence of multiple pregnancies has increased significantly since the late 20^th century.⁴ Several factors have contributed to this, but the two most dominant ones are the rising maternal age at the time of conception and the use of assisted reproductive technology (ART), including in vitro fertilisation (IVF) and fertility drugs. Other factors include previous pregnancy history, family history, and genetics. There is a higher possibility of having multiple pregnancies if you are one yourself or if it runs in your family (generally through the maternal side of the family).

The use of ART can increase the risk of having multiple pregnancies because the process can sometimes involve the transfer of more than one embryo into the woman’s uterus to increase the chances of having a successful pregnancy. To reduce the risks and complications associated with multiple pregnancies, some countries have put regulations around the number of embryos that can be transferred at once during the IVF process.

Risks associated with multiple pregnancies

Despite the advancements in perinatal/neonatal medicine, multiple pregnancies present several challenges both during pregnancy and the postpartum period. It is therefore essential to discuss the risks of multiple pregnancies as they are associated with a higher neonatal and maternal morbidity and mortality rate, preterm delivery, and low birth weight, amongst many other high-risk morbidities.⁵ Improving outcomes involves reducing the rate of preterm births, providing a conducive environment in the uterus for the foetus to grow, and maximising neonatal care and neonatal ICU, if required.

Multiple-foetus pregnancies significantly increase the risks of complications compared to singleton pregnancies. They carry an increased risk of pregnancy-related issues;

• some include hypertensive issues
• gestational diabetes mellitus
• hyperemesis
• preterm labour
• anaemia
• placental abruption
• increased risk of C-section
• and prolonged hospital stay, amongst many others

Over 60 percent of twins and most higher-order multiples are premature; the higher the number of foetuses, the greater the risk of preterm delivery.⁶ 

Premature labour and birth are the most common complication of multiple pregnancies. Premature labour is classed as a delivery that occurs before the gestational age of 37 weeks. This has a significant impact on the health and weight of the babies. Women carrying multiple foetuses are more likely to have their babies preterm than a singleton pregnancy.

Pre-eclampsia is also a common complication that results from high blood pressure developed during pregnancy, called gestational hypertension. Women pregnant with more than one foetus are twice as likely to develop high blood pressure-related complications with more severe symptoms than women with only one. This condition is often detected earlier in pregnancy.

There are also increased foetal and neonatal morbidity and mortality risks linked to multiple gestation pregnancies. This correlates with an increased risk of preterm delivery, low birth weight, and intrauterine growth restriction.

However, the neonatal mortality rate in multiple foetus pregnancies is similar to singletons, increasing with decreasing gestational age.⁷ Neonatal outcomes at specific gestational ages and birth weights in these pregnancies are also known to be similar to those of singletons. 

There is a close correlation between birth weight and gestational age. An increase in the number of preterm babies directly relates to the rate of reduced birth weights in multiple pregnancy births, thereby increasing the incidence of neonatal intensive care unit admission, respiratory distress syndrome, and long-term developmental issues.⁸

These neonates also have an increased incidence of intrauterine growth retardation.⁹ It is difficult to make a direct comparison between specific morbidities and mortality in these pregnancies due to several other contributing factors. 

Management and prevention

An effective management plan for multiple pregnancies will be based on the following:

• Pregnancy, overall health, and medical history
• Number of foetuses
• Reaction to specific medication, procedures, or intervention
• Personal preference
• Expectations for the course of pregnancy

Managing pregnant people with multiple pregnancies will include a team of specialists, including an obstetrician, midwife, and sonographer with expertise in multiple pregnancy scanning. Other specialists that may be required include dieticians, perinatal mental health teams, physiotherapists, and infant feeding specialists.¹⁰ Facilities for onward referral should also be available if required. 

Due to the increased risk of complications, more frequent visits may be required to help the healthcare provider prevent or detect complications early and start effective treatment or management. The nutritional status and weight of the pregnant woman will also be monitored more closely than for singleton pregnancies, as the woman will require more calories, protein, and other nutrients. The healthcare provider may also recommend reduced activity as it is known to benefit the mother and the growing foetuses.

Some women may need bed rest either at home or in the hospital, depending on the number of foetuses and the presence of any complication. No evidence shows that preventive bed rest prevents preterm birth in multiple pregnancies.¹¹

Summary

To conclude, multiple pregnancies pose an increased risk of complications, but they can be limited by following adequate prenatal care that includes: increased nutrition, adequate rest, stress management, and sometimes medical intervention to prevent preterm birth and cervical cerclage. Early detection and management are key to increasing the chances of having a safe and successful delivery and healthy babies. Healthcare providers, therefore, play a crucial role in guiding expectant mothers through their multiple pregnancies.